Cast iron containing lamellar graphite (gray cast iron) is used, for example, in motor vehicle construction. Such cast iron is thus used as a material for casting clutch disks, flywheels, brake drums and disks, exhaust manifolds, and the like.
Because of the high thermal stresses to which such motor car parts are subjected, they have to be resistant to temperature changes to the same extent as they have to be resistant to wear and breakage.
For all intents and purposes, cast iron which is resistant or immune to thermal shocks or considerable thermal changes does not exist per se. The cast iron material which best meets the particular requirements must rather be determined by optimizing the strength characteristics, the composition, and grain structure in dependence upon the particular requirements.
The phenomena which takes place in the cast iron as the result of the stresses due to temperature changes and due to the temperature change itself are highly complex. On account of rapidly changing temperature differences, stresses and grain structure changes occur in the cast object. The latter, in turn, have a tendency to change the characteristics of the material and, since they are mostly associated with volume changes, additional stresses may be caused which then lead to cracks and fissures in the cast objects.